1. Technical Field
The present invention relates to data communication systems, identification tags and methods of notifying an elapsed time period
2. Related Art
Conventionally, “best-before” dates of food and drinks, “expiration dates” of commuter passes, and “return time” limits of rental articles, etc. are printed on articles and/or their containers, or lending forms affixed to articles, in the form of characters showing dates that indicate time limits. The time limits can be learned by reading them.
However, according to such a display method, in order to know if the time limit has passed, or the time limit approaches, the date displayed needs to be recognized as characters and compared with a present date to make a judgment. For this reason, it was difficult to make such a judgment instantaneously.
In this regard, a method has been proposed in which a commuter pass is equipped with a display device, and the display device is made to display an alert message when its expiration is approaching (for example, Japanese Laid-open Patent Application HEI 10-305680).
However, according to the method indicated in Japanese Laid-open Patent Application HEI 10-305680, an alert is notified through an automatic ticket machine by passing the above-described commuter pass through the automatic ticket machine, and therefore this method is not applicable when a ticket gate without an automatic ticket machine is used, and is difficult to be applied to other usages, such as notifications of best-before dates of food and drinks, return time limits of rental articles, etc.
The present invention has been made in view of the problems described above, and an object is to provide data communication systems, identification tags, and elapsed time notification methods, which enable visual and instantaneous recognitions of best-before dates, expiration dates, etc. in various usages.